Method for thermal processing a semiconductor wafer

ABSTRACT

A method for thermal processing a semiconductor wafer is disclosed. A rapid thermal processing (RTP) chamber encompasses a heating means, a rotation means, and a cooling system for cooling walls of said RTP chamber. A semiconductor wafer is loaded into the RTP chamber just being cooling down to a first temperature by using the cooling system. When loading the semiconductor wafer, it has a temperature that is lower than the first temperature, thereby causing a tendency of particle deposition from the walls of the RTP chamber onto the semiconductor wafer. The semiconductor wafer is pre-heated to a second temperature higher than the first temperature with the heating means, thereby eliminating the tendency of particle deposition. Upon reaching the second temperature, the rotation means is activated to start to rotate the semiconductor wafer, while the semiconductor wafer being ramped up to a third temperature.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to rapid thermal processing (RTP) ofsemiconductor wafers and, more particularly, to a radiation-first RTPmethod for uniformly thermal-processing a rotating semiconductor wafer.

2. Description of the Prior Art

Rapid thermal processing (hereinafter referred to as “RTP”) methods andRTP systems are known in the art. A RTP chamber refers to a device thatrapidly heats objects, such as semiconductor wafers. Such devicestypically include a substrate holder for holding a semiconductor waferand an energy source for heating the wafer. During heat treatment, thesemiconductor wafers are heated under controlled conditions according toa pre-set temperature regime. For monitoring the temperature of thesemiconductor wafer during heat treatment, thermal processing chambersalso include radiation sensor devices, such as pyrometers, that sensethe radiation being emitted by the semiconductor wafer at a selectedwavelength. By sensing the thermal radiation being emitted by the wafer,the temperature of the wafer can be calculated with reasonable accuracy.

The thrust of the work was increasing the temperature uniformity, anddeveloping heating cycles and processes which decreased the thermalbudget. Prior art RTP chambers can heat unstructured, homogeneousmaterials in the form of a flat plate or disk, and produce temperatureuniformities across the plate adequate for semiconductor processingprocesses.

The wafers are generally inserted into a chamber with at least someportions of the chamber walls transparent to transmit radiation frompowerful heating lamps. These lamps are generally tungsten-halogenlamps, but arc lamps or any other source of visible and/or near infraredradiation may be used. The radiation from the lamps is directed throughthe transparent portions of the walls on to the surface of the wafer tobe heated.

FIG. 1 shows a cross-sectional sketch of a prior art RTP chamber 10 witha wafer 12 supported by quartz pins 14 in position for heating byradiation from a set of lamps 16 and 18. The chamber 10 is supported bya housing 20 having highly polished interior walls 22. A door 24 is usedto make a gas tight seal for the chamber 10. The temperature of thewafer 10 is measured by a pyrometer 26. A computer 32 receives thetemperature reading from the pyrometer 26, and controls the lamps 16 and18 to heat the wafer 12 according to a preprogrammed schedule. Thecomputer 32 also serves to control a gas flow controller 30, whichintroduces process gas 28 into the chamber 10.

Rotation of susceptors bearing wafers is well known as a means ofensuring uniform heating and growth of films in semiconductor processes.FIG. 2 depicts a flow chart according to a prior art RTP method. Afterloading the wafer into the cooled down RTP chamber (Step 42), the wafer,which is supported by the quartz pins and has a temperature (typicallyroom temperature) that is lower than the chamber walls that are justcooled down to about 30-80° C., starts to rotate (Step 44). Processinggas, if necessary, is then flowed into the chamber (Step 46). A pre-setheating program, which is stored in and executed by the computer, isthen activated to heat the wafer in either a soak mode or a spike modefor a pre-selected time period (Step 48). However, the prior art methodfor thermal processing a wafer arises particle problems.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide aradiation-first RTP method for solving the particle problems.

According to the claimed invention, a method for thermal processing asemiconductor wafer is disclosed. A rapid thermal processing (RTP)chamber comprising at least a radiation source for heating an object, arotation means for rotating the object, and a cooling system for coolingwalls of the RTP chamber is prepared. A semiconductor wafer is loadedinto the RTP chamber. At this point, the walls of the RTP chamber havejust been cooling down to a first temperature by using the coolingsystem. The semiconductor wafer is then pre-heated to a secondtemperature with the radiation source. The second temperature is higherthan the first temperature. Upon reaching the second temperature, therotation means is just activated to start to rotate the semiconductorwafer that is disposed on quartz pins, while the semiconductor waferbeing ramped up to a third temperature of 700-1100° C.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings:

FIG. 1 is a schematic, cross-sectional diagram showing a prior art RTPchamber with a wafer supported by quartz pins in position for heating byradiation from a set of lamps;

FIG. 2 depicts a flow chart according to a prior art RTP method;

FIG. 3 is a flow chart of the radiation-first RTP method in accordancewith one preferred embodiment of the present invention;

FIG. 4 is a Temperature vs. Time plot illustrating a RTP heating programin a “soak” mode in accordance with this invention; and

FIG. 5 is a Temperature vs. Time plot illustrating a RTP heating programin a “spike” mode in accordance with this invention.

DETAILED DESCRIPTION

The present invention pertains to a newly designed radiation-first RTPmethod for alleviating or eliminating particle problem thereof. Asmentioned, rotation of susceptors bearing wafers is employed touniformly heat wafers. After thermal processing a wafer, a succeedingwafer, which is typically transported at room temperature, is loadedinto the cooled down RTP chamber.

In order to speed up the throughput of the volume production of ICs andsome other reasons, the RTP chamber are ordinarily cooled down to abouta temperature of about 30-80° C., instead of room temperature. Upon theloading of the succeeding wafer, the susceptor starts to rotate.Processing gas, if necessary, is then flowed into the chamber. A pre-setheating program, which is stored in and executed by a computer, is thenactivated to heat the wafer in either a “soak” mode or a “spike” modefor a pre-selected time period, for example, 30-90 minutes.

It is discovered that after batches of wafers for RTP heat treatment,the interior walls of the RTP chamber would absorb and accumulateparticles. It is further discovered by the inventor that the prior artrotation-first RTP sequence would cause the particles to move fromhotter walls of the RTP chamber to a relatively colder surface of therotating wafer just loaded into the RTP chamber, and thus contaminatingthe wafer. The tendency of particles deposition on the colder surfacesof the wafer at the earlier stage of the RTP treatment adversely affectsthe preciseness and accuracy of the subsequent lithographic processesand hence deteriorates the quality of the integrated circuits. It is onepurpose of the present invention to eliminate such tendency.

The radiation-first RTP method according to this invention is carriedout in a RTP system that is capable of thermal processing thesemiconductor wafer while rotating the wafer. Such RTP system isavailable from Applied Materials, Inc., Mattson Technology, Inc., orSteag AST, among others. For example, the radiation-first RTP method ofthis invention can be performed in a Steag AST 3000 RTP tool. Typically,such RTP tool comprises a RTP chamber, wherein one wall of the chambersupporting a wafer rotates with respect to the rest of the chamber sothat the wafer being treated in the RTP chamber is relatively rotatedwith respect to the radiation source such as halogen lamps or tungstenlamps that heats the wafer. The walls of the RTP chamber have at least aportion transparent to the radiation from the halogen lamps.

Please refer to FIG. 3. FIG. 3 is a flow chart of the radiation-firstRTP method in accordance with one preferred embodiment of the presentinvention. As shown in FIG. 3, the radiation-first RTP method startswith Step 152: loading a wafer into a RTP chamber as described. Thewafer is supported with quartz pins that are disposed in the RTPchamber. Before rotating the wafer, a pre-set heating program that isstored and executed in a computer of the RTP tool is activated. Thecomputer controls a rotation means, power of radiation source, andflowrate of a processing gas.

The pre-set heating program includes a pre-heat stage that rapidlyraises the temperature of the static (not-rotating) wafer from T₁ (aboutroom temperature) to a higher temperature T₂ ranging between 100° C. and250° C. (Step 154). According to this invention, the pre-heat stage iscontrolled by a close-loop and heated at a fixed power, and it usuallytakes about 5-30 seconds to reach T₂. Since the walls of the RTP chamberare cooled by a cooling water system, the temperature of the walls isnot raised up as fast as the wafer does. The walls of the RTP chambernow become relatively colder than the surfaces of the wafer after thepre-heating of the wafer.

Upon reaching T₂, the present invention method immediately proceeds toStep 156: starting to rotate the wafer and ramping the temperature up tothe highest temperature T₃ ranging between about 700° C. and about11001° C. The rotation of the wafer may be driven by mechanical meanssuch as a combination of shaft and gear drive, or by other means such asmagnetic means, or gas-driven. According to the preferred embodiment ofthis invention, the rotation speed of the wafer is about 70-85 rpm. Itis noted that the rotation means will not be activated until thepre-heating of the wafer is completed.

In Step 156, the temperature of the wafer continues to be raised up fromT₂ to T₃ at the above-mentioned fixed power. The exact temperature valueof T₃ depends upon the purposes of the RTP treatment. Typically, T₃ranges between 700° C. and 1100° C., but should not be limiting.

There are two ordinary RTP modes, which are so-called “soak” mode and“spike” mode, which are depicted in FIG. 4 and FIG. 5, respectively. Thetiming of activating the rotation means of the RTP system is alsoindicated. In FIG. 4, after the temperature reaches T₃, the temperatureis maintained and fixed at this temperature for a time period of, forexample, 30-90 minutes, as a plateau region that can be seen in thisfigure. After this, the wafer is cooled down to 30-80° C. (Step 158). InFIG. 5, a “spike” mode RTP heating program is illustrated. Whenemploying the “spike” mode, there is no such plateau region as shown inFIG. 4. After reaching T₃, the wafer is immediately cooled down to30-80° C. in the spike RTP.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A method for thermal processing a semiconductor wafer, comprising:providing a rapid thermal processing (RTP) chamber comprising at least aradiation source for heating an object, a rotation means for rotatingsaid object, and a cooling system for cooling walls of said RTP chamber;loading a semiconductor wafer into said RTP chamber just being coolingdown to a first temperature by said cooling system; pre-heating saidsemiconductor wafer to a second temperature with said radiation source,wherein said second temperature is higher than said first temperature;and upon reaching said second temperature, activating said rotationmeans to start to rotate said semiconductor wafer, while saidsemiconductor wafer being ramped up to a third temperature.
 2. Themethod for thermal processing a semiconductor wafer according to claim 1wherein said pre-heating step is completed in 30 seconds.
 3. The methodfor thermal processing a semiconductor wafer according to claim 1wherein said first temperature ranges between 30-80° C.
 4. The methodfor thermal processing at semiconductor wafer according to claim 1wherein said second temperature ranges between 100-250° C.
 5. The methodfor thermal processing a semiconductor wafer according to claim 1wherein said third temperature ranges between 700-1100° C.
 6. The methodfor thermal processing a semiconductor wafer according to claim 1wherein said rotation means is a mechanical rotation means including acombination of shaft and gear drive.
 7. The method for thermalprocessing a semiconductor wafer according to claim 1 wherein saidrotation means is a magnetic rotation means.
 8. The method for thermalprocessing a semiconductor wafer according to claim 1 wherein saidrotation means is gas-driven.
 9. The method for thermal processing asemiconductor wafer according to claim 1 wherein said RTP chamberfurther equipped with a computer that controls said rotation means,power of said radiation source, and flowrate of a processing gas. 10.The method for thermal processing a semiconductor wafer according toclaim 1 wherein said third temperature is maintained for a pre-selectedtime period.
 11. The method for thermal processing a semiconductor waferaccording to claim 1 wherein upon reaching said third temperature, saidsemiconductor wafer is immediately cooled down.
 12. The method forthermal processing a semiconductor wafer according to claim 1 whereinsaid radiation source comprises halogen lamps and tungsten lamps.
 13. Amethod for thermal processing a semiconductor wafer, comprising:providing a rapid thermal processing (RTP) chamber comprising at least aheating means, a rotation means, and a cooling system for cooling wallsof said RTP chamber; loading a semiconductor wafer into said RTP chamberjust being cooling down to a first temperature by said cooling system,wherein when loading said semiconductor wafer, it has a temperature thatis lower than said first temperature, thereby causing a tendency ofparticle deposition from said walls of said RTP chamber onto saidsemiconductor wafer; pre-heating said semiconductor wafer to a secondtemperature higher than said first temperature with said heating means,thereby eliminating said tendency of particle deposition; and uponreaching said second temperature, activating said rotation means tostart to rotate said semiconductor wafer, while said semiconductor waferbeing ramped up to a third temperature.
 14. The method for thermalprocessing a semiconductor wafer according to claim 13 wherein saidpre-heating step is completed in 5-30 seconds.
 15. The method forthermal processing a semiconductor wafer according to claim 13 whereinsaid first temperature ranges between 30-80° C.
 16. The method forthermal processing a semiconductor wafer according to claim 13 whereinsaid second temperature ranges between 100-250° C.
 17. The method forthermal processing a semiconductor wafer according to claim 13 whereinsaid third temperature ranges between 700-1100° C.
 18. The method forthermal processing a semiconductor wafer according to claim 13 whereinsaid heating means comprises halogen lamps and tungsten lamps.